A variable valve operating mechanism such as that shown in FIG. 18 is described in Japanese Patent Application Publication No. JP-A-11-324625. This variable valve operating mechanism 100 is provided with a valve operating member 102 for opening and closing a valve 101, and a camshaft 103 which is rotated by a crankshaft. A drive cam 104 and a swing cam 106 are provided on the camshaft 103, and a cam surface 105 which engages with the valve operating member 102 is formed on the swing cam 106. An arm 109 is supported on a control shaft 107 via a variable cam 108, and the both ends of the arm 109 are connected to the drive cam 104 and the swing cam 106 by links 110, 111. The displacement of the swing cam 106 is modified in accordance with the operating conditions of an internal combustion engine by varying the angle of the arm 109 using the variable cam 108.
Japanese Patent Publication No. 3485434 describes a variable valve operating mechanism for an internal combustion engine having two intake valves and two exhaust valves per cylinder, in which two drive cams 104 and two swing cams 106 are provided on a camshaft 103, similarly to JP-A-11-324625. By dissimilating the profiles of the two drive cams 104 or dissimilating the profiles (the shapes of cam surfaces 105) of the two swing cams 106, a difference in lift can be applied to the two valves 101, so that a swirl is generated in the cylinder, and thus the fuel consumption is improved.
Japanese Patent Application Publication No. JP-A-2004-138000 describes a variable valve operating mechanism in which two drive cams are provided on a camshaft for each cylinder, a control shaft and a gear mechanism are incorporated into the camshaft for varying the relative phase of the drive cams, two swing arms are provided on a support shaft for each cylinder, two control shafts and a gear mechanism are incorporated into the support shaft for varying the relative phase of the swing arms, and the three control shafts are controlled individually by actuators, so that a difference in lift is applied to the two valves in each cylinder.
However, according to the variable valve operating mechanisms of Japanese Patent Application Publication No. JP-A-11-324625 and Japanese Patent Publication No. 3485434, the drive cam 104 and swing cam 106 are both provided on the control shaft 103, and hence a power transmission path extending from the drive cam 104 to the valve operating member 102 is complicated. Further, the power transmission path is closed by the links 110, 111, and therefore a large load acts on the control shaft 107 as the drive cam 104 rotates. Accordingly, a large hydraulic or electric device must be used as the actuator for driving the control shaft 107, and the high output of this large actuator leads to an increase in power loss in the internal combustion engine. As a result, the valuable swirl effect attenuates, leading to deterioration of the fuel consumption.
According to the variable valve operating mechanism of JP-A-2004-138000, a difference in lift is applied to the two valves by varying the relative phase of the two drive cams and the relative phase of the two swing arms. Therefore, a control shaft and a gear mechanism must be incorporated into both the camshaft and the support shaft, and individual actuators are required for the three control shafts. As a result, the overall number of components in a variable device increases, and complications arise in both structure and control.